We got this unit off craigslist a couple years ago. It had died on them and then it sat for 10 years or so. We got it back to his shop and reassembled and started playing. First thing I did was make a acrylic window that would go in one of the accessory ports and coat a stub with phosphor from a fluorescent lamp. Putting this in the chamber allows visual confirmation of the electron beam and if it is actually scanning. It did show a raster where the e-beam was causing the phosphor to fluoresce and the size of the pattern changed with the magnification control and also changed with the scan rate selector.

From this and the fact we had a raster and characters on the CRT we had a pretty good indication that it was mostly working, it was just we were not getting a signal out of the PMT on the Secondary Electron Detector (SED). Eventually I figure out there is no power to the PMT and no power coming out of the HV power supply inside the console. I then notice that in the middle of the cable to the SED there is a wad of electrical tape. Apparently when this machine was moved in the past some idiot just cut the cable instead of disconnecting it in the console. When they put it together they just twisted the wires together and put electrical tape over it. Eventually the tape broke down under the +500v and shorted out taking out the HV power supply.

The HV power supply is pretty simple, just a high frequency flyback oscillator that drives a small transformer and is then rectified and filtered. When the cable was shorted the output diode eventually failed. Since the transformer was warm I had pretty good reason to believe that the power supply was still functioning so we ordered a couple HV rectifier diodes. When they came in I installed it and shortened the cable to get rid of the splice and the SEM came up.

The following image was one of the first ones out of it, the end of a hair. At this point the final aperture strip was not in place so the depth of field is very shallow. To capture the image we put a camera above the imaging CRT and opened the shutter and hit the photo button on the console. The Photo CRT is a low persistence phosphor CRT and the image is slowly scanning over the surface to create the image.